This standard specifies the reference method and routine method for determining the titratable acidity of milk powder. This standard is applicable to the determination of titratable acidity of milk powder. GB/T 5413.28-1997 Determination of titratable acidity of milk powder GB/T5413.28-1997 Standard download decompression password: www.bzxz.net

GB/T5413.28—1997
This standard provides two methods. Method 1 is equivalent to the International Dairy Federation standard IDF86:1978 "Determination of Milk Powder (Benchmark Method)"; Method 2 is equivalent to the International Dairy Federation standard IDF81:1981 "Milk Powder Standard Method)".
Method 1 of this standard is the arbitration method.
From the date of implementation, this series of standards will replace GB5413-85. This standard is proposed by the China Light Industry General Association.
This standard is under the jurisdiction of the National Dairy Standardization Center. The responsible drafting unit of this standard: National Dairy Quality Supervision and Inspection Center. Titrate acidity
-Determination of titratable acidity (common
The drafting organizations of this standard include: Food Hygiene Supervision and Inspection Institute of the Ministry of Health, Light Industry Research Institute of Zhejiang Province, Harbin Morinaga Dairy Co., Ltd., Nestle (China) Investment Services Co., Ltd. The main drafters of this standard include: Huang Min, Wang Yun, Li Yuxian. 334
1 Scope
National Standard of the People's Republic of China
Determination of titratable acidity
Milk powder--Determination of titratable This standard specifies the reference method and routine method for determining the titratable acidity of milk powder. This standard is applicable to the determination of the titratable acidity of milk powder. 2 Definitions
This standard adopts the following definitions.
Acidity of milk powder
GB/T5413.28—1997
Replaces GB5413--85
The number of milliliters of 0.1 mol/L sodium hydroxide solution required to titrate 100 mL of reconstituted milk with a dry matter content of 12% with 0.1 mol/L sodium hydroxide solution until the pH reaches 8.3 or the solution turns pink (phenol crisp indicator). Method Reference Method
3 Principle of Method
A certain amount of milk powder is dissolved in water to make reconstituted milk, which is then titrated with 0.1 mol/L sodium hydroxide to a pH of 8.3. The number of milliliters of 0.1 mol/L sodium hydroxide solution consumed can be calculated. Calculate the amount of sodium hydroxide required to titrate 100mL of reconstituted milk with a dry matter content of 12%. The amount of sodium hydroxide solution required varies as the natural buffering substances in the product become acidic or as the amount of acidic or alkaline substances added. 4 Reagents
All reagents, unless otherwise specified, are of analytical grade; all experimental water, unless otherwise specified, refers to grade tertiary water. 4.1 Sodium hydroxide standard solution: c(OH-) is 0.1±0.0002mol/L. Protect this solution from carbon dioxide penetration. Calibration of sodium hydroxide standard solution: Weigh approximately 0.18g of potassium hydrogen phthalate dried to constant weight at 105~110℃, accurate to 0.1mg, dissolve in 50mL of carbon dioxide-free water in a conical flask, add two drops of 5g/L phenolic acid indicator, and titrate with the prepared sodium hydroxide solution until pink, and perform a blank experiment at the same time. The concentration of the sodium hydroxide standard solution is: c(NaOH) = (V,-V,)× 0. 2042
Wherein: c(NaOH)——concentration of sodium hydroxide, mol/L; m-weight of potassium hydrogen phthalate, g; V, amount of sodium hydroxide solution, mL;
V2-amount of sodium hydroxide solution in blank test, mL. (1)
4.2 Phenolyl solution: Dissolve 0.5g phenolphthalein in 75mL 95% ethanol by volume, add 20mL water, then add sodium hydroxide solution (4.1) until it turns pink immediately after adding one drop, then add water to make up to 100mL. 4.3 Nitrogen.
Approved by the State Administration of Technical Supervision on May 28, 1997 and implemented on September 1, 1998
5 Instruments
Common laboratory instruments and:
5.1 Balance: sensitivity is 0.01g or higher. GB/T5413.28—1997
5.2 Burette: 0.1mL scale, accurate to 0.05mL. 5.3 pH meter: with glass electrode and appropriate reference electrode, calibrated with pH6 and pH9 buffer solutions. Readable to 0.01pH unit. 5.4 Magnetic stirrer. wwW.bzxz.Net
5.5 Measuring cylinder: 100mL.
5.6 Conical flask: 250mL, with ground and ground glass stopper, neck can accommodate electrodes, burette head and a nitrogen tube. 6 Operation steps
6.1 Sample preparation
Move all samples into a clean and dry container (with a sealed lid) about twice the volume of the sample, immediately cover the container, and repeatedly rotate and shake to mix the sample thoroughly. During this operation, the sample should be avoided from being exposed to the air as much as possible to minimize the absorbed moisture. 6.2 Determination
6.2.1 Weigh 4 g of sample (6.1) into a conical flask (5.6). Accurate to 10 mg. 6.2.2 Using the dosage form (5.5), measure 96 mL of water at about 20°C to reconstitute the sample (6.2.1), stir vigorously, and then let it stand for 20 minutes. 6.2.3 Use a burette (5.2) to drop sodium hydroxide solution (4.1) into the conical flask until the pH reaches 8.3 (determined by a pH meter). During the titration, always stir with a magnetic stirrer (5.4) and blow nitrogen into the conical flask to prevent the solution from absorbing carbon dioxide in the air. The entire titration process should be completed within 1 minute. Record the number of milliliters of sodium hydroxide solution used, accurate to 0.05 mL. 7 Expression of analysis results
The titrated acidity of the sample (°T) = ×10××12m ×(1 -w)
Wherein: c——the concentration of the sodium hydroxide standard solution, mol/L; V—the number of milliliters of the NaOH solution used during titration (6.2.3), mL; m—the mass of the weighed sample, g
w—the mass fraction of water in the sample, %; 12—12g of milk powder is equivalent to 100mL of reconstituted milk (skim milk powder should be 9, and skim whey powder should be 7). The result is retained to one decimal place.
Note: If the acidity of the sample is expressed by lactic acid content, then: the lactic acid content of the sample (g/100g) = T×0.009. T is the titrated acidity of the sample (°T); 0.009 is the conversion factor of lactic acid, that is, 1mL of 0.1mol/L sodium hydroxide standard solution is equivalent to 0.009g of lactic acid. 8 Allowable difference
The repeatability of this method is that the difference between the results of two separate tests on the same sample made by the same analyst at the same time or within a short time interval shall not exceed 1.0°T.
Method 2 Conventional method
9 Principle of the method
Dissolve a certain amount of milk powder in water to make reconstituted milk. Use phenolic acid as an indicator and cobalt sulfate as a reference color, and titrate with 0.1mol1. sodium hydroxide standard solution until pink. According to the number of milliliters consumed, the amount of sodium hydroxide required to titrate 100mL of reconstituted milk with a dry matter content of 12% can be calculated.
GB/T5413.281997
The amount of sodium hydroxide solution required varies with the acidification of the natural buffer substance in the product or the amount of acidic or alkaline substances added. 10 Reagents
All reagents, if not specified, are of analytical grade; all experimental water, if not specified otherwise, is grade tertiary water. 10.1 Sodium hydroxide standard solution: c(OH-) is 0.1±0.0002mol/L. Calibration is the same as 4.1. 10.2 Reference solution: Dissolve 3g of cobalt sulfate heptahydrate (CoSO·7H,0) in water and make up to 100mL. 10.3 Phenol solution: the same as 4.2.
11 Instruments
Common laboratory instruments and:
11.1 Analytical balance.
11.2 Burette: The scale is 0.1mL and can be accurate to 0.05mL. 11.3 Pipette: 2mL.
11.4 Measuring cylinder: 100mL.
11.5. Conical flask: 250mL, with ground-mouth and ground-mouth glass stopper. 12
Operation steps
12.1 Sample preparation
Transfer all samples into a clean, dry container (with a sealed lid) twice the volume of the sample, immediately cover the container, and repeatedly rotate and oscillate to mix the sample thoroughly. During this operation, the sample should be kept from being exposed to the air as much as possible to minimize the amount of water absorbed. 12.2 Sample weighing
Weigh 4g of sample (12.1) into a conical flask (11.5), accurate to 10mg. 12.3 Determination
12.3.1 Use the measuring tube (11.4) to measure 96mL of water at about 20℃, stir vigorously to restore the sample (12.2), and then let it stand for 20min. 12.3.2 Add 2-3mL of reference solution (10.2) Get the standard color and gently rotate to mix. If a series of similar products are to be measured, this standard solution can be used for the entire measurement process, but not more than 2 hours. 12.3.3 Add 2mL of phenolic acid solution (10.3) to the second conical flask and gently rotate to mix. 12.3.4 Use a burette (11.2) to add sodium hydroxide solution (10.1) to the second conical flask, rotating the flask while adding until the color is similar to that of the standard solution and does not fade within 5 seconds. The entire titration process should be completed within 45 seconds. Record the number of milliliters of sodium hydroxide solution used, accurate to 0.05mL. 13 Expression of analysis results
The titrated acidity of the sample (T) = ×10××12m x (lw)
Wherein: c-concentration of sodium hydroxide standard solution, mol/L; V—--the number of milliliters of sodium hydroxide solution used during titration (12.3.4), mL; m—the mass of the sample weighed, g;
w——the mass fraction of water in the sample, %; 12--12g milk powder is equivalent to 100mL reconstituted milk (skim milk powder should be 9, skim whey powder is 7). The result is retained to one decimal place.
Note: If the acidity of the sample is expressed by lactic acid content, then: the lactic acid content of the sample (g/100g) = T×0.009. T is the titrated acidity of the sample (T); 0.009 is the conversion factor of lactic acid, that is, 1mL of 0.1mol/l. sodium hydroxide solution is equivalent to 0.009g lactic acid. 337
14 Allowable difference
GB/T5413.28-1997
The repeatability of this method is that the difference between the results of two separate tests on the same sample made by the same analyst at the same time or within a short time interval shall not exceed 1.0T.
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